The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, an internal combustion engine is an apparatus that operates using energy from heat generated by burning a gas mixture in a combustion chamber. As an internal combustion engine, a multi-cylinder engine with a plurality of cylinders for increasing power and reducing noise and vibration is generally used.
Recently, a cylinder deactivation apparatus of an engine that improves fuel efficiency by deactivating some of a plurality of cylinders in an engine when the engine generates a small amount of power has been developed with the increase in energy cost.
A way of deactivating cylinders used by such a cylinder deactivation apparatus is to operate an engine by injecting and burning a gas mixture in only some of the plurality of cylinders without injecting and igniting a gas mixture in the other cylinders.
For example, for a four-cylinder engine, the apparatus does not inject and ignite a gas mixture in two cylinders and operates the engine with only the other two cylinders.
Meanwhile, a variable valve lift technique that selectively implements a zero lift of a valve so that a gas mixture is not injected may be applied to deactivated cylinders.
However, abrasion of the pad portion may be occurred when a pad portion of a valve opening/closing unit is in rolling-contact with a zero cam or a camshaft to realize zero lift of a valve. Durability of the valve opening/closing unit may be deteriorated if the pad portion of the valve opening/closing unit is worn. In addition, if the pad portion is worn, reliability about cylinder deactivation may be deteriorated as the valve opening/closing unit makes a lever motion depending on rotation of a cam even while the valve opening/closing unit is operated so as to realize the zero lift of the valve.